This invention relates to combustors for gas turbine engines and particularly to means for reducing the smoke density of the exhaust emitted therefrom.
U.S. Pat. No. 3,498,055 granted to W. W. Mieczhowski, Jr. and myself on Mar. 3, 1970 and assigned to the same assignee addresses a similar problem and provides a solution by adding plunged holes to admit a critical amount of air to the primary combustion zone. The array of plunged holes is located on the liner of the burner can and is placed downstream of the fuel nozzle but within the primary combustion zone. This forms a single bank of plunged holes sized to provide the critical amount of air.
While the suggested arrangement of plunged holes and the critical air flow values may have been effective for smoke reduction in certain applications, this solution has not proven to be viable for other combustors.
We have found that we can obtain a relatively smokeless burner from an existing burner configuration while maintaining the necessary performance parameters which are acceptable for use in a gas turbine engine and without compromising burner efficiency. Unlike the means for reducing smoke emission in the structure described in U.S. Pat. No. 3,498,055, supra, we found that adding less than 6% air to the primary combustion zone proved to be critical for efficient combustion where the smoke emissions were sufficiently reduced and without impairing the other necessary burner operating parameters. As a matter of fact, to operate the burner and introduce a larger percentage of air would induce lean blowouts and render the combustor unsatisfactory for aircraft application.
Additionally, the judicial location of the holes and the number of holes have proven to be of significant consequence. For example, it was found that the proper introduction of air could not be emitted from a single bank of rows of holes and spaced rows of circumferential holes was necessary to the proper operation of the burner. The hole location between banks also proved to be critical to burner operation while effectuating smoke reduction.